Computer hard drives typically employ a number of rapidly rotating disks having a coating of magnetic data storage material. Each disk is matched with a magnetic read/write head which is held very close to the disk surface. The magnetic read/write head can thereby read and write data on the magnetic disk as it moves.
The magnetic head is prevented from contacting the disk surface by an air cushion of moving air which is moving with the disk. Typically, the magnetic head rests about 0.02 microns above the disk while the disk is moving.
It is very important that the magnetic head and disk surface not come in contact for any extended period of time, since this can result in damage to both the disk surface and the magnetic head. For example, data can be permanently destroyed if excessive contact should occur. In an operating hard drive, contact is prevented by the fact that the disks are rapidly moving.
It is also important for the magnetic head and disk surface not to come in contact when the disks are not rotating (i.e., when the hard drive is not powered). If a disk and magnetic head are at rest and in contact for a period of time, the head and disk surface can stick together, resulting in damage to the disk surface when the disks start to rotate. Also, the disk must start from rest, and a certain minimum velocity is required for the magnetic head to float over the disk surface. Therefore, each startup of the hard drive results in the magnetic head and disk surface rubbing for a distance until the disk achieves sufficient speed to form the air cushion.
For these reasons, load/unload ramp structures have been used in some hard drives to hold the magnetic heads away from the disk surfaces while the hard drive is not operating. The magnetic heads are released from the ramp structure when the disks have achieved the minimum speed for causing the magnetic heads to float above the disk surfaces.
It is noted that some hard drives have disks with nonstick portions that will not cause damage to the magnetic heads even if the heads remain in contact with the nonstick portion for an extended period of time. Such hard drives are known as contact start/stop (CSS) hard drives. CSS hard drives do not utilize load/unload ramp structures.
FIG. 1 shows a typical prior art hard drive with three disks 2. An actuator arm 3 supports a suspension 4, a slider 5 and a lifting feature 6. A magnetic read/write head (not shown) is located on a bottom surface of the slider 5. The actuator arm 3 pivots about a pivot post 9. The lifting feature 6 is positioned on the suspension 4 so that it engages with a ramp 8 on a ramp structure 10. The ramp 8 imparts an upward force on the lifting feature 6 which lifts the slider 5 and magnetic head away from the disk 2. The magnetic head is thereby not in contact with the disk 2 whenever the lifting feature 6 is moved onto the ramp 8.
It is desirable to make the ramp structure 10 from low friction polymer materials. Low friction ramps 8 reduce the amount of energy required to unload the magnetic heads (a concern during unpowered unloading), and also reduce the amount of debris particles generated when the lifting feature rubs over the surface of the ramp. It is also desirable to rigidly fix the location of the ramp structure with respect to the disk surface.
Ramp structures 10 made of polymer materials have thermal expansion coefficients which are often quite different from the thermal expansion coefficients of surrounding metal components which are usually made of aluminum or stainless steel. Therefore, during temperature changes, the plastic ramp structure expands and contracts at a different rate than surrounding components, resulting in misalignment of the ramp structure 10 relative to the disks 2.
Thermal expansion induced misalignment results in decreased usable disk surface area for data storage.
Thermal expansion induced misalignment also necessitates looser alignment tolerances between the ramps 8 and disks 2, which requires that more vertical space be provided between disks. An undesirable consequence of this is that fewer disks fit into a hard drive of a given size.
U.S. Pat. No. 4,933,785 to Morehouse et. al. discloses a ramp structure having a cam structure for holding magnetic heads in an unloaded position. Morehouse does not disclose means for preventing thermal expansion induced misalignment.
U.S. Pat. No. 5,034,837 to Schmitz discloses a ramp structure comprising a single piece of plastic. Schmitz does not disclose means for preventing thermal expansion induced misalignment.
U.S. Pat. No. 5,241,438 to Matsushima discloses a ramp structure comprising a plastic ramp and rigid metal ramp support member for supporting the plastic ramps. Matsushima does not disclose means for preventing thermal expansion induced misalignment.
It would be an advance in the art of hard drive design to provide a ramp structure which provides constant ramp alignment over a wide range of temperatures.